I'm not sure. Vitamin deficiency causes neurological issues like balance and control.
It's hitting most of your birds, If it's not mold or toxicity, it could be disease. But I don't know which one.
Way too much grubs and grains, it should be half that, once a week.
Can you check their run for anything moldy?
Are they vaccinated for Mereks?
What layer pellets?
Best case is vitamin deficiency.